Impact of organic solvents on lipid-extracted microalgae residues and wastewater sludge co-digestion

This study investigates the combined production of lipids and biogas via anaerobic mono- and co-digestion of microalgae biomass grown in municipal untreated wastewater. In the co-digestion assays, extracted microalgae and wastewater sludge were mixed at different ratios: 25–75, 50–50, and 75–25% total volatile solids (VS) of each substrate, respectively. The neutral and polar fatty acid methyl esters constituted approximately 13 and 1.5% of the total lipids, respectively. Mono-digestion of lipid-extracted microalgae had a lower biochemical methane potential (BMP) than of non-extracted microalgae. Organic solvents were shown to negatively impact both mono- and co-digestion of extracted microalgae. Co-digestion experiments showed synergy between sludge and microalgae residues, increasing the BMP from 91.4 Normalized mL (NmL) CH4/g VS in the mono-digestion of evaporated extracted microalgae up to 228.6 NmL CH4/g VS in the co-digestion of the mixture with 25% VS of microalgae biomass with 75% VS of sludge.